The present invention relates to an auto-control device for controlling the operation of a lift pump subject ot the detection result of a temperature sensor, which automatically detects the temperature of the lift pump.
When a lift pump is operated, a circuit breaker is commonly installed in the coil of the motor of the lift pump to automatically cut off power supply when the coil is overloaded. The maximum load of the coil of the motor is generally set at 75.degree. C. , that is when the temperature of the coil of the motor reaches 75.degree. C. , the circuit breaker automatically cuts off power supply from the circuit. The rising of the temperature of the coil of the motor to as high as 75.degree. C. generally occurs a certain length of time after an idle running of the lift pump. If power supply is not cut off from the lift pump when the lift pump is overloaded due to an idle running, the lift pump will be burnt out. However, even if a circuit breaker is installed, the vanes of the lift pump will wear away quickly when the lift pump frequently runs idle. When the vanes of the lift pump begin to wear, the lift pump will consume much electric current to provide the same amount of water lifting power. In consequence, a longer length of time is needed to trigger the circuit breaker when the lift pump is overloaded. There is also known a water-pressure controlled auto-control device for use with a lift pump. This structure of water pressure switch, which can be triggered to automatically turn on the motor of the pump by water pressure. However, if the water tap of the water tank is opened when the water level of the water tank drops below the drain port of the pump or the water tank is empty, the pump will run idle, and the pressure switch can not be reset to automatically turned off the pump after the water tap is closed. When this situation happens, the pump will be burnt out.
The present invent on has been accomplished under the circumstances in view. It is one object of the present invention to provide a lift pump auto-control device which eliminates the aforesaid problems. It is another object of the present invention to provide a lift pump auto-control device which automatically turns off the lift pump when the temperature of the lift pump surpasses a predetermined high temperature level, and which automatically turns off the lift pump when the temperature of the lift pump drops below a predetermined low temperature level. It is still another object of the present invention to provide a lift pump auto-control device which is easy to install. It is still another object of the present invention to provide a lift pump auto-control device which needs little installation space.
According to one aspect of the present invention, the lift pump auto-control device comprises a housing fastened to the outside wall of the lift pump by a double-sided annular adhesive tape, and a sensor mounted inside the housing by a locating block to detect the temperature of the lift pump. According to another aspect of the present invention, the sensor automaticlly cuts off power supply from the lift pump when the temperature of the lift pump surpasses 50.degree. C., and automatically turns on the lift pump when the temerpature of the lift pump drops below 28.degree. C. According to still another aspect of the present invention, a spring member is mounted inside the housing to give a downward pressure to the sensor, so that the temperature detecting side is of the sensor is maintained closely in contact with the outside wall of the lift pump. According to still another aspect of the present invention, a heat-insulative ring is mounted within the housing around the sensor so that the sensor effectively detects the temperature of the lift pump. According to still another aspect of the present invention, epoxy resin is filled from the wire hole on the housing into the inside of the housing to bond the internal parts of the lift pump auto-control device firmly together and simultaneously to seal off water.